This article examines what is said to be un/known about obesity and the ways in which attributions of knowledge or ignorance circulate in the field of public health nutrition. Risks caused by individual behaviors have been an overstated concern in public health. Obesity, like many of today's complex problems, is determined by myriad nested interactions spanning the political economies of market regulation, modes of agricultural production, the biochemistry of appetite regulation, and changing family structures. Yet public intervention-and the science produced to validate it-remains wedded to a mode of intervening that has limited purchase on the complexity with which it contends. This article draws on scholarship on the social construction of ignorance to argue that the field of evidence in obesity science is fashioned in a way that deflects attention (and responsibility) away from questions of food production and marketing and continues to frame the problem as one of individual responsibility. Rather than discrediting the veracity of evidence produced out of industry-research partnerships that increasingly dominate public health research, this article examines how the field of evidence has been structured by these relations. It argues that the demonstration of causal relations between political and socioeconomic determinants of malnutrition and measurable health indexes is largely impossible, not simply because of the absence of good evidence but because the existing parameters of good science cannot straightforwardly reveal such relations. This, in turn, is due to the configuration of the knowable in terms of whether knowledge can be made operational. © 2016 by the American Anthropological Association.